Magnetron



Dec. 17, 1946.

E. D. M ARTHUR 2,412,824

MAGNETRON Filed June 22, 1942 2 Sheets-Sheet .1

Fi I.

3:. 70 J) 7/ z I, 40

Inventor:

His Attorney.

Dec. 17, 1946. E. D. MGARTHUR MAGNETRON Filed June 22, 1942 2 Sheets-Sheet 2 U w :r M IA W 0c n m i eD fi v W h .5 M? E which the current supply quency fields generated by Patented Dec. 17, 1946 Elmer D. McArthur,

New York Schenectady, N. Y., to General Electric Company.

assignor a corporation of Application June 22, 1942, Serial No. 447,903

9- Claims.

The present invention relates to improvements in high frequency electronic devices of the magnetron type. a

As is well-known, the functioning of a magnetron as a generator of high frequency waves depends upon the combined action of appropriately directed electric and magnetic fields upon electrons which move in an interelectrode space. In general, the frequency of the waves which may be developed by such devices is a function of the strength of the magnetic field employed, the required field strength being higher for the higher frequencies. Because of this relatlonship,

have heretofore been required to be associated with massive magnetic structures, leading to a cumbersome construction for the apparatus as a whole.

It is a primary object of the present invention to provide an improved type of ultra-high frequency magnetron in which the weight and size of the operative parts, including especially the magnetic elements, are reduced to a minimum.

In general this object is realized by the use of a construction in which the magnetic field is produced by permanently magnetized pole pieces locatedwithin a container which consists wholly or in part of ferromagnetic components arranged to provide a return path for magnetic flux traversing the pole pieces. In this Way, with the electrodes of the device located Within the conmagnetrons which are operable in the ultra-high frequency band tainer in appropriate proximity to the pole pieces,

it proves possible to obtain intense magnetic fields in the interelectrode space without the use of a separately excited electromagnet or other external appurtenances. in weight and has the further advantage that its magnetic components may be adjusted in the factory for best operation with the assurance that no further adjustment will be required in the field.

A further important feature of the improved construction consists in wires for the cathode are introduced through the center of one of the magnetic pole pieces in a manner which avoids coupling the cathode circuit to the high frethe operation of the magnetron.

The features of the invention desired to be protected herein are pointed out in the appended claims. The invention itself, together with its further objects and derstood by reference to the following description taken in connection with the drawings in which Fig. 1 is a vertical section of a magnetron device suitably embodying the invention; Fig. 2'

is a transverse sectional view serving to illustrate the anode structure employed in the device of Fig. 1; Fig. 3 is an enlarged view in partial sec- The resultant structure is light.

an arrangement by.

advantages may best be unare used to receive rings tion of the cathode of the device of Fig. 1; Fig. 4 is a detail view of one of the structural elements of the device of Fig. 1; Fig. 5 is a longitudinal section of a modification of the invention; Fig. 6 is a longitudinal section illustrating a further modification, and Fig. 7 is a perspective of one element of the device of Fig. 6.

Referring particularly to Fig. 1 there is shown an elongated cylindrical container, the lateral wall structure of which is provided by a single metal tube terial such as cold rolled steel or the like. The ends of the container are closed byfianged members H and I2 which are welded or otherwise hermetically joined to the inner surface of the part III. The outer surface of the envelope is provided with a series of circumferentially extending fins I4 which are adapted to serve as heat dissipating elements and a somewhat larger circular element l5 provided near the upper end of the container acts as a mounting 'fiange for the device as a whole. (Any number of additional cooling fins may be used, as required.)

Within the container and approximately at its central region there is provided an anode structure 20 shown in plan view in Fig. 2. This comprises a circular member which has a relatively large central opening 22 and a series of smaller openings 23 arranged symmetrically about the central opening. The central opening is joined to the openings 23 by means of radially extending slots 25.

The structure 20, which preferably consists of terior Wall surface of the part l0. To facilitate the brazing operation, small channels 28 are cut in the outer periphery of the structure and these of brazing material applied before the anode structure is inserted within the container. A relatively large circumferentially extending channel 29 serves to reduce the overall weight of the structure.

Within the opening 22 of the anode structure there is provided an indirectly heated cathode comprising asleeve 32 of nickel or other suitable material having flanges 32' spun up at its extremities. This sleeve, which may be coated externally with a suitable activating material such as barium oxide, contains a filamentary heater 34 by which it may be maintained at an emissive temperature. One end of the cathode sleeve is closed by a metal disk 36 while an apertured disk 31 partially closes its other extremity.

In the operation of the device a space charge is assumed to be developed in thespace between the structure by the application of a suitable potential impressed between one of the cathode lead-in wires 31 and 31" and the container Ill to which the 3 0 18 structure is directly conductively con- IU consisting of ferromagnetic manected. The electrons coupled resonant units in each of which in-.

ductance is provided by the wall surface bounding one of the circular openings 23 and capacitance is provided by the opposing surface of one of the slots 25. Taking this viewpoint, it will be seen that the operating frequency is in a large measure determined by the dimensions of the openings 23.

For the purpose of providing a magnetic field of suflicient intensity to permit the apparatus to function in its intended fashion, there are provided within the container I tapered magnetic pole pieces 4|] and 4| which are directed axially of the container and which extend in close proximity to the upper and lower surfaces of the anode structure 20. For present purposes these pole pieces are assumed to be permanently magnetized in such a sense that the north pole of one faces the'south pole of the other.

In order to assure the existence of a magnetic field of the required intensity the pole pieces 40 and 4| should be constituted of a magnetizable substance having a high coercive force and a high energy factor. One of the materials which may be used in this connection is that known as Alnico, meaning a particular class of alloys of aluminum, nickel and cobalt. Alloys of this type are described, for example, in Tokuschichi Mishima Patents 2,027,994 to 2,028,000 inclusive and are further described in W. E. Ruder Patents 1,947,274 and 1,968,569. Other magnetic materials which may be employed are alloys of iron, nickel and titanium as described, for example, in Honda Patents 2,105,652 and 2,105,658.

If the pole pieces 40 and 4| are constituted of Alnico, which'is considered to be a preferred material, they are normallyprepared in cast form and have their critical surfaces finished by grinding. The ground surfaces may include, for example, the end surfaces of both pole pieces and the peripheral surfaces indicated by the numerals 44 and 45 respectively. These latter surfaces, to-

gether with the end surfaces which adjoin themmay advantageously be copper plated to reduce losses attributable to high frequency circulating currents induced by the proximity of these surfaces to the interelectrode spaces in which high frequency waves are generated.

In order to provide a low reluctance connection between the base extremities of the respective pole pieces and the lateral wall of the container, the pole pieces may be respectively seated upon relatively thick disk-like members 48 and 49 consisting of ferro-magnetic material such as steel. For the purpose of securing the pole pieces fixedly to these basing members, use may be made of clamping rings and 52 slipped over the pole pieces and welded to the basing members. Each basing member is of such diameter as to fit snugly within the tubular container part III so as to provide a low reluctance connection with that part, and-is welded to one of the closure members||,|2.

Accurate spacing of the pole pieces 40 and 4| with reference to the anode structure 20 may be obtained by the use of spacing rings 54 and 55 used in the manner indicated. As is 8.130!!! in Fig. 1, each of these rings is interposed between one surface of the anode structure and the surface of an apertured disk 56, 51, each disk in tum being in abutment with an appropriately formed shoulder provided on the adjacent pole piece as indicated at 58 and 59. The spacing rings 54 and 55 may be welded in place before the pole pieces are inserted within the container.

With the pole pieces 40 and 4| arranged inside the container In it becomes convenient to use the pole pieces as a supporting means for the cathode structure 32. This may be done, for example, by the use of a pair of insulating beads 62 and 63 which are respectively centered in axially extending openings 65 and 66 cut in the pole pieces. The lower bead 63 is provided with a central apertureadapted to receive a. centering stud 68 projecting downwardly ,from the cathode end plate 36. The upper head 62 has two separate openings 10 and H through which the current supply wires 31' and 31" extend. These wires, which are held in spaced relation within the channel 65 by means of additional insulators 16 and 11, are joined at their extremities to relatively heavy lead-in wires 19 and 80. These in turn are sealed into the container through a glass-to-metal seal which comprises a body of glass 8| fused to the extremity of a metal eyelet 82. This arrangement of the cathode supply leads has the particular advantage that it avoids any substantial coupling between the cathode supply circuit and the high frequency fields generated in the interelectrode space, thus being a consequence of the fact that :both the supply leads extend axially with respect to the electrode structures and are fully shielded by the body of the pole piece 40.

In fabricating the construction of Fig. 1 the anode structure 20 is first positioned within the container part l0 and secured in place. Thereafter, the spacing rings 54 and 55 are inserted and finally the pole pieces and their associated basing structures are put in place. The cathode 32 may be preliminarily assembled with the pole piece 40 before that part is lowered into the container. After the closure members II and |2 have been welded in, the container may be evacuated through an exhaust tabulation 85, which is then sealed off as indicated at 86.

To permit the evacuation of all parts of the container, it is necessary to provide suitable passageways connecting the various sections of the enclosed space. To this end, the disk-like members 48 and may be provided with radially extending slots such as the slot 49' which is illustrated in Fig. 4 in connection with the part 49. In this way the channel 66 is enabled to communicate with the space outside the pole piece 4| through the channel 49', and a similar connection with reference to the channel 65 is provided by the corresponding slot in the part 48. With the same object in view, openings may be provided in the positioning disks 56 and 51. An opening 92 provided in one surface of the anode structure 20 makes the channel 29 accessible to the .evacuatingsystem.

, After the container is fully evacuated and sealed off, the pole pieces 40 and 4| may be magnetized in a known manner by being placed in a magnetic field of suitable intensity. It is an advantage of the illustrated construction that for each partic-.- ular device the degree of magnetization of the pole pieces can be adjusted in the factory to a value which assures the most satisfactory operation of the device as a whole. Since all the parts 5 of the tube structure are fixed and since no external magnetic appurtenances have to be added in the field, installation and use of these tubes is greatly simplified.

When a device such as that illustrated in Fig.

1 is placed in operation, it is, of course, necessary to provide some means for abstracting a portion of the energy developed in the interelectrode space. This may be done in one way by an arrangement which includes a coupling loop I introduced through an opening I02 in the wall of the anode structure. The coupling loop in the arrangement shown has an extension in the form of a wire I04 which constitutes the inner conductor of a coaxial transmission line having a tubular part I05 as its outer conductor. The tube I05 passes through the wall of the container cylinder I 0 and may be exteriorly connected through a tapering enlargement I01 with a somewhat larger tubualr part I08. In similar fashion, the wire I04 is merged into a larger conductor I09 through a tapered transition region II 0 which is of such configuration as to avoid any substantial change in the characteristic impedance of the line. (The fulfillment of this latter condition requires the maintenance of a constant ratio between the diameters of the outer and inner conductors.) The conductors I08 and I09 may connect with an antenna or other agency for utilizing the high frequency energy developed by the apparatus, and their size is determined with this end in view. The vacuum tightness of the container is preserved by means of a head of glass II2 which forms a seal between the conductor I09 and the surrounding tubular member I08.

In an arrangment such as that of Fig. 1 in which the cathode is not at ground potential it is necessary to provide an insulating transformer in connection with the supply of filament heating current. In order to avoid this requirement it is preferable in some instances to employ a structure in which the cathode is grounded to the structure of the enclosure and to adopt provisions for insulating the anode from ground. This possibility is illustrated; in Fig. 5.

In the figure last referred to the magnetic structure is of the same general character as that described in connection with Fig, 1 and comprises permanently magnetized pole pieces I 20 and HI which are enclosed within a metallic con tainer I22 consisting of ferromagnetic material. The pole pieces have a low reluctance magnetic connection with the structure of the enclosure so that a return path is provided for the magnetic flux.

The anode structure, which is indicated at I24, is functionally similar to the anode 20 of Fig. 1, being provided internally with a plurality of resonant cavities (not shown) which have a resonant frequency corresponding to the desired frequency of operation of the apparatus. The structure is insulated from the metallic enclosure I22 and from the other parts of the device by means of glass insulators I26 and I21 which serve also as seal-in means for anode terminals I 28 and I29. These terminals are associated with cup-like members I30 and I3I which are sealed into the glass rings I26 and I21 respectively, the rings in turn being supported from metal eyelets I33 and I34 secured to the outer surface of the enclosure. Heavy conductive rods I36 and I31 extending between the anode structure I24 and the cap members I 30 and I 3I afford a rigid support for the anode structure.

Power is assumed to be taken out of the anode 6 structure by means of a coupling loop, which, however, does not appear in the particular view of the structure which is afforded by Fig. 5.

The cathode, which extends centrally through 5 the anode structure I24, comprises an emissive tubular part I3 9-which terminates in flanges I40 and I40. A heater (not shown) is arranged within the part I39 and serves to maintain it at emissive temperature. The cathode flange I 40 is seated in an. appropriately formed recess provided in the lower extremity of the pole piece I so that the cathode is electrically grounded to the magnetic structure. A lead-in wire I 4| which extends axially through the pole pieces I20 and through an 15 insulating bead I42 at the upper end of the oathode make it possible to supply heating current to the cathode filament, a return path for this current being provided through the grounded structure of the cathode proper.

It is not essential that a magnetron produced in accordance with the invention be symmetrical with respect to a central transverse plane, and the alternative embodiment of Fig. 6 represents a construction in which this condition is not fulfilled. In this case a permanently magnetized pole piece I50 is enclosed within a ferromagnetic container I5I which forms part of the magnetic circuit. The pole piece I50 is based upon a ferromagnetic header I53 which closes the upper end of the container I5I and is partially supported within the container by means of a non-magnetic ring I54. A cathode structure I51 depends centrally from the lower extremity of the pole piece I50, being insulated from the pole structure by means of an interposed insulating element indicated at I58. Potential and heating current are supplied to the cathode through lead-in wires I59.

Below the cathode I51 there is provided a multicavity anode I62 which is shown in perspective detail in Fig. 7. This anode is formed of magnetic material (e. g., iron or steel) so that it serves not only as an anode but also as a oom plementary pole piece for the magnetic pole I50.

- However, it is not necessarily permanently mag-' netized. The exposed surfaces of the anode are 'coated, by plating or otherwise, with copper r other highly conductive material adapted to permit the free circulation of high frequency currents. The whole anode structure is based upon the bottom closure I63 of the container so that a complete magnetic circuit is provided through the container walls.

As appears most clearly in Fig. 7 the anode is provided with a number of radially extending circular channels I65 which communicate with the space'above the anode through slots I 66. The channels and the slots connect at their inner ends with an opening I61 formed centrally in the (so anode structure. By virtue of this arrangement the anode is enabled to function as a multi-cavity resonator adapted to be excited by the rotating space charge developed in proximity to its upper surface by the electrons emitted from the cathode 0.; I51. The high frequency energy thus developed in the resonant cavities may be utilized externally by the use of a coupling loop (not shown) extending into one of the cavities in the manner indicated in Fig. l.

The arrangement of Fig. 6 has the particular advantage that no significant magnetic gap exists between the anode I62, viewed as a magnetic pole piece, andv thesource of the electrons desired to be afiected by the magnetic field. Because of this circumstance the effective reluctance of the total magnetic path is reduced. This discharge devices having transversely extending anode cavity constructions such as those illustrated by Figures 6 and '1 since the invention illustrated thereby is covered broadly by certain claims in my pending application Ser. No. 674,194, filed June 4, 1946, and constituting a continuation in part of the application for this patent.

While the invention has been described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. I therefore aim in the appended claims to cover all such equivalent variations as come within the. true spirit and scope of the foregoing disclosure.

-What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electronic device comprising a container forming the envelope of said device and having a part of its wall structure constituted of ferromagnetic material, means including a permanently magnetized pole piece within said container for producing a magnetic field in a particular region of the enclosed space; and cooperating electrode elements located in the said magnetic field, said pole piece having a direct magnetic connection "with the ferromagneticpart of said wall structure and forming therewith a low reluctance path which is-closed except for region of said electrodes.

2. An electronic device comprising an evacuated'container having its walls constituted mainly of ferromagnetic material, means including a permanently magnetized pole piece within the container for producing a localized magnetic field,

' a ferromagnetic member supporting said pole piece and providing a direct magnetic connection between the pole piece and a ferromagnetic'portion of the wall of the container, whereby a low reluctance return pathis provided for magnetic flux traversing the pole piece, and mutually cooperating discharge electrodes in proximity to said pole piece and within the influence of the said magnetic field.

3. A magnetron device comprising a container forming an envelope of the device and having its lateral walls constituted principally of ferromagnetic material, ferromagnetic members extending transversely of said container and presenting surfaces within the container, a pair of magnetic pole pieces in mutually spaced relation within said container, said pole pieces being respectively supported by said ferromagnetic members, whereby a low reluctance fiux path between the remote extremities of said pole pieces is provided through said members and. through. the lateral walls of the container, and cooperating electrode elements positioned in the space between said pole pieces.

4. Electronic apparatus comprising a container having a substantial part of its wall structure constituted of ferromagnetic material, means including a permanently magnetized pole piece within said container for producing a magnetic field therein, said pole piece having a low reluctance connection with the wall structure of said container whereby said wall structure provides a return path for magnetic flux traversing the pole piece, and an anode and a cathode in proximity to said pole piece and within the influence of said magnetic field, said cathode comprising an equipotential emitting part, a filamentary heater for, said part and a pair of current supply wires for said heater extending axially through one of said pole pieces and sealed through a wall of said container.

5. An electronic discharge device including an elongated cylindrical container forming the envelope of said device and having its lateral walls constituted principally of ferromagnetic material, ferromagnetic members closing the ends of the container, a pair of magnetic pole pieces'respectively supported from said members in mutually spaced relation within said container and in magnetic contact with said members, and cooperating electrodes within said container and in the space between said pole pieces.

6. A magnetron device comprising a container providing the envelope of said device and including a hollow cylinder of ferromagnetic material, a self-resonant anode structure supported within said cylinder intermediate its ends, a cathode structure concentric with said anode structure, and magnetic pole pieces within said container adjacent the ends thereof and on opposite sides of said anode structure, each of said pole pieces having a direct ferromagnetic connection with said cylinder whereby the combination of said cylinder and said connections provides a low reluctance return path for magnetic flux traversing the pole pieces.

'7. An electronic device comprising an elongated container forming the envelope of said de-- vice and having a part of its wall structure connant anode structure within said container and intermediate the ends thereof, a cathode in cooperatively spaced relation with respect to said anode structure, magnetic pole pieces within said container'on opposite sides of said anode structure and having a low reluctance connection with said container, and spacing means interposed between said anode structure and said pole pieces maintaining them in a predetermined structural relationship.

8. A magnetron comprising an evacuated c tainer constituted principally of ferromagnetic metal, electrodes cooperatively spaced within said container, one of said electrodes being connected directly to the container, another of said electrodes being supported in insulating relationship to said container, and mean including a permanently magnetized element within said container for producing a magnetic field in the space between said electrodes, said container having a direct ferromagnetic connection with said element to provide a low reluctance return path for 

